There is a shaft seal device as a prior art related to the present invention which seals a chemical fluid or the like. This shaft seal device is employed for providing a seal in a clearance gap on the periphery of a rotary shaft of various kinds of compressors or the like (see, for example, Japanese Laid-Open Patent Publication No. 2000-179702 (FIG. 1)). Action fluid which is used as a refrigerant medium for a compressor of automobiles or the like operates as a high pressure sealed fluid in the cavities disposed around the rotary shaft. Sealed fluid, not limited to the refrigerant medium, cannot prevent some impurities from being included during its circulatory action. These impurities, in particular, easily get caught onto the seal faces. Some particular chemical fluid may allow solidification of the impurities after getting caught to the seal faces. Further, the high pressure sealed fluid forces seal lips providing a seal against the sealed fluid in the circumference of a rotary shaft to press against the diameter surface of the rotary shaft. While rubber-made seal lips or resin-made seal lips receive a high pressure from sealed fluid while making a secure contact with the rotary shaft, a problem will arise in case of inclusion of impurities wherein the impurities attracted to the seal faces accelerate abrasion of the sliding seal faces.
This shaft seal device 100 is constructed as shown in FIG. 6. FIG. 6 is a cross-sectional view of a half portion of the shaft seal device 100. The shaft seal device 100 includes a fit engagement member 102 of cylindrical design which has three undulated seal portions 107 along outer circumference thereof. The fit engagement member 102 disposes a reinforcement annulus 103 therewithin in an integral structure. The fit engagement member 102 is provided with reinforcement from the reinforcement annulus 103 so as to form a secure contact with a bore surface (hereafter simply referred to as a bore) 112 of housing 111. Also a first seal lip 101 extends from the fit engagement member 102 in radially inward a direction. In addition, there is disposed a resin-made second seal lip 108 in the external environment side (left side in the figure) with respect to the first seal lip 101. Between the rubber-made first seal lip 101 and the resin-made second seal lip 108 there is disposed a backup ring 106 which is made of thin sheet metal. The second seal lip 108 is secured by means of a fixture member 109 between the backup ring 106 and the fixture member 109. The first seal lip 101 made of rubber material is susceptible to leak of the sealed fluid and the backup ring 106 is intended for preventing such leak of the sealed fluid. Therefore the backup ring 106 is disposed between the first seal lip 101 and the second seal lip 108, being responsible for a full load exerted from the external environment side. When the first seal lip 101, the second seal lip 108 and the backup ring 106 are pressed against the rotary shaft 113 due to the pressure of the sealed fluid, this will increase a possibility of rapid abrasion of the rotary shaft 113. The sealed fluid also tends to include various kinds of impurities during its operation as action fluid. The impurities included in the sealed fluid are caught on the seal faces of the respective seal lips 101, 108 which come to a contact with the rotary shaft 113. Also a particular composition contained in the sealed fluid may be solidified due to friction heat, which is deposited on the seal faces of the respective seal lips 101, 108 and causes abrasion of opposing slide faces.
However, the backup ring 106 in the form of thin sheet metal does not have enough strength to be able to keep the first seal lip 101 in tight contact under a small area pressure with the rotary shaft 113. While the first seal portion 104A is urged to press against the rotary shaft 113 strongly by the pressure of the sealed fluid, the backup ring 106 is urged to press against the rotary shaft 113 as well by the sealed fluid. This implies that the seal portion 104A and the backup ring 106 will be worn through sliding against the rotary shaft 113. Further, the entire seal face of the second seal face 108 having a tight contact with the rotary shaft 113 is subject to abrasion over wide areas. In a particular case that the sealed fluid is used under a high pressure, the first seal lip 101 and the second seal lip 108 are heavily urged against the rotary shaft 113 by the sealed fluid so that the respective, relative slide faces will undergo substantial abrasion. If impurities included in the sealed fluid are deposited on the seal face, abrasion of the seal face will progress even faster. Such abrasion of the respective slide faces will deteriorate seal performance of the shaft seal device 100. Although the shaft seal device 100 is configured replaceable for a replacement due to abrasion, the rotary shaft 130 is hard to be replaced because of its elongated form as well as its integral structure with the apparatus.
The present invention is introduced to alleviate the above mentioned problems. A primary technical goal which this invention tries to achieve is to protect the slide faces of the seal lips in a shaft seal device from abrasion caused by impurities included in a sealed fluid or a kind of sealed fluid which is solidified through chemical reaction due to friction heat, and to enhance seal performance of the shaft seal device by preventing abrasion of the surface of a rotary shaft which slides relative to the seal lips. Another goal is to improve durability of the rotary shaft and to reduce a replacement cost of the rotary shaft by preventing abrasion thereof.